In recent years, commercialization of automotive vehicles or hybrid vehicles having an idle stop function has been developed as the demand for improved fuel economy increases. In these vehicles, pumps driven by an internal combustion engine are to stop at the time when the internal combustion engine is stopped, and therefore the presence of a pump-driving source other than the internal combustion engine has been needed. In particular, automotive vehicles, hybrid vehicles and the like having an idle stop function require an oil pump so that a hydraulic mechanism for controlling an automatic transmission can keep ensuring a hydraulic pressure. In view of the above, there has been developed the trend toward the increase of the use of an electric oil pump which imparts a rotational force to a pump rotor by using an electric motor to cause pumping actions.
As an electric oil pump mounted to an automatic transmission of an automotive vehicle, there has widely been adopted an internal gear pump of a trochoid type. In an internal gear pump, a pump rotor is rotated by a driving rotational shaft driven by a motor, so that an outer rotor having an inner tooth engageable with an outer tooth of the pump rotor is rotated. With this, the volume of a plurality of volume chambers formed between the inner tooth of the outer rotor and the outer tooth of the pump rotor is continuously changed thereby performing intake/discharge of a hydraulic oil. Such an internal gear pump is disclosed in Japanese Patent Application Publication No. 2012-207638 (Patent Document 1) for example.
A typical electric oil pump is provided including: a drive control part for controlling the passage of electric current through an electric motor; a stator section having a wire and an iron core for generating magnetomotive force by the electric current passage from the drive control part; a rotor section disposed in a space defined by the inner periphery of the stator section and having a permanent magnet to be rotated by the magnetomotive force; a driving rotational shaft fixed to the rotor section by means of press-fitting or the like so as to rotate together therewith; and a pump rotor section fixed to the driving rotational shaft by means of press-fitting or the like so as to rotate together with the driving rotational shaft. Incidentally, the stator section and the rotor section are parts constituting an electric motor.